The present invention relates to a cam mechanism for moving a lens of a camera.
Generally, in a camera, in order to drive a lens group along an optical axis in accordance with the photographer's intention, a cam mechanism is provided. The cam mechanism has a cam groove formed in a cam ring, which engages a cam follower secured to a lens frame. Upon rotation of the cam ring about the optical axis, the lens frame is moved in the direction of the optical axis, thereby accomplishing the zoom function.
In one known mechanism, the cross sectional shape of the cam groove is a trapezoid, i.e., a truncated V-groove. That is, the channel is flat and narrow at the bottom, with sides sloping from a wider entrance. The trapezoidal shape is determined by manufacturing reasons. The cross sectional shape of a tip of the cam follower pin is a truncated cone of the same approximate size as the cam groove, and therefore corresponds to the shape of the cam groove.
In this conventional arrangement, manufacturing or assembly error may cause misalignment of the cam groove and the cam follower. If the alignment of the cam groove and the cam follower differs from the relation as designed, an uneven and unstable distribution of forces may result. The uneven and unstable distribution of forces can further result in uneven or localized wear of the cam follower groove, and uneven and unstable torque. The lens may move erratically, and the unstable movement may worsen over time.